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Update #0 - First Release
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LAX1DUDE
448
sources/main/java/com/google/common/base/Objects.java
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448
sources/main/java/com/google/common/base/Objects.java
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/*
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* Copyright (C) 2007 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.common.base;
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import static com.google.common.base.Preconditions.checkNotNull;
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import java.util.Arrays;
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import javax.annotation.CheckReturnValue;
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import javax.annotation.Nullable;
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import com.google.common.annotations.GwtCompatible;
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/**
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* Helper functions that can operate on any {@code Object}.
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*
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* <p>
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* See the Guava User Guide on <a href=
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* "http://code.google.com/p/guava-libraries/wiki/CommonObjectUtilitiesExplained">writing
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* {@code Object} methods with {@code Objects}</a>.
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*
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* @author Laurence Gonsalves
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* @since 2.0 (imported from Google Collections Library)
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*/
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@GwtCompatible
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public final class Objects {
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private Objects() {
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}
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/**
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* Determines whether two possibly-null objects are equal. Returns:
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*
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* <ul>
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* <li>{@code true} if {@code a} and {@code b} are both null.
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* <li>{@code true} if {@code a} and {@code b} are both non-null and they are
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* equal according to {@link Object#equals(Object)}.
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* <li>{@code false} in all other situations.
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* </ul>
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*
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* <p>
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* This assumes that any non-null objects passed to this function conform to the
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* {@code equals()} contract.
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*/
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@CheckReturnValue
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public static boolean equal(@Nullable Object a, @Nullable Object b) {
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return a == b || (a != null && a.equals(b));
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}
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/**
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* Generates a hash code for multiple values. The hash code is generated by
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* calling {@link Arrays#hashCode(Object[])}. Note that array arguments to this
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* method, with the exception of a single Object array, do not get any special
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* handling; their hash codes are based on identity and not contents.
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*
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* <p>
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* This is useful for implementing {@link Object#hashCode()}. For example, in an
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* object that has three properties, {@code x}, {@code y}, and {@code z}, one
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* could write:
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*
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* <pre>
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* {@code
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* public int hashCode() {
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* return Objects.hashCode(getX(), getY(), getZ());
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* }}
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* </pre>
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*
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* <p>
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* <b>Warning</b>: When a single object is supplied, the returned hash code does
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* not equal the hash code of that object.
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*/
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public static int hashCode(@Nullable Object... objects) {
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return Arrays.hashCode(objects);
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}
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/**
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* Creates an instance of {@link ToStringHelper}.
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*
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* <p>
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* This is helpful for implementing {@link Object#toString()}. Specification by
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* example:
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*
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* <pre>
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* {@code
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* // Returns "ClassName{}"
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* Objects.toStringHelper(this)
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* .toString();
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*
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* // Returns "ClassName{x=1}"
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* Objects.toStringHelper(this)
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* .add("x", 1)
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* .toString();
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*
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* // Returns "MyObject{x=1}"
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* Objects.toStringHelper("MyObject")
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* .add("x", 1)
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* .toString();
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*
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* // Returns "ClassName{x=1, y=foo}"
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* Objects.toStringHelper(this)
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* .add("x", 1)
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* .add("y", "foo")
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* .toString();
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*
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* // Returns "ClassName{x=1}"
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* Objects.toStringHelper(this)
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* .omitNullValues()
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* .add("x", 1)
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* .add("y", null)
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* .toString();
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* }}
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* </pre>
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*
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* <p>
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* Note that in GWT, class names are often obfuscated.
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*
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* @param self the object to generate the string for (typically {@code this}),
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* used only for its class name
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* @since 2.0
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*/
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public static ToStringHelper toStringHelper(Object self) {
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return new ToStringHelper(simpleName(self.getClass()));
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}
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/**
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* Creates an instance of {@link ToStringHelper} in the same manner as
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* {@link Objects#toStringHelper(Object)}, but using the name of {@code clazz}
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* instead of using an instance's {@link Object#getClass()}.
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*
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* <p>
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* Note that in GWT, class names are often obfuscated.
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*
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* @param clazz the {@link Class} of the instance
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* @since 7.0 (source-compatible since 2.0)
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*/
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public static ToStringHelper toStringHelper(Class<?> clazz) {
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return new ToStringHelper(simpleName(clazz));
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}
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/**
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* Creates an instance of {@link ToStringHelper} in the same manner as
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* {@link Objects#toStringHelper(Object)}, but using {@code className} instead
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* of using an instance's {@link Object#getClass()}.
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*
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* @param className the name of the instance type
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* @since 7.0 (source-compatible since 2.0)
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*/
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public static ToStringHelper toStringHelper(String className) {
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return new ToStringHelper(className);
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}
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/**
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* {@link Class#getSimpleName()} is not GWT compatible yet, so we provide our
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* own implementation.
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*/
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private static String simpleName(Class<?> clazz) {
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String name = clazz.getName();
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// the nth anonymous class has a class name ending in "Outer$n"
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// and local inner classes have names ending in "Outer.$1Inner"
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name = name.replaceAll("\\$[0-9]+", "\\$");
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// we want the name of the inner class all by its lonesome
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int start = name.lastIndexOf('$');
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// if this isn't an inner class, just find the start of the
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// top level class name.
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if (start == -1) {
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start = name.lastIndexOf('.');
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}
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return name.substring(start + 1);
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}
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/**
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* Returns the first of two given parameters that is not {@code null}, if either
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* is, or otherwise throws a {@link NullPointerException}.
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*
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* <p>
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* <b>Note:</b> if {@code first} is represented as an {@link Optional}, this can
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* be accomplished with {@linkplain Optional#or(Object) first.or(second)}. That
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* approach also allows for lazy evaluation of the fallback instance, using
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* {@linkplain Optional#or(Supplier) first.or(Supplier)}.
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*
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* @return {@code first} if {@code first} is not {@code null}, or {@code second}
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* if {@code first} is {@code null} and {@code second} is not
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* {@code null}
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* @throws NullPointerException if both {@code first} and {@code second} were
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* {@code null}
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* @since 3.0
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*/
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public static <T> T firstNonNull(@Nullable T first, @Nullable T second) {
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return first != null ? first : checkNotNull(second);
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}
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/**
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* Support class for {@link Objects#toStringHelper}.
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*
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* @author Jason Lee
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* @since 2.0
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*/
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public static final class ToStringHelper {
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private final String className;
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private ValueHolder holderHead = new ValueHolder();
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private ValueHolder holderTail = holderHead;
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private boolean omitNullValues = false;
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/**
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* Use {@link Objects#toStringHelper(Object)} to create an instance.
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*/
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private ToStringHelper(String className) {
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this.className = checkNotNull(className);
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}
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/**
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* Configures the {@link ToStringHelper} so {@link #toString()} will ignore
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* properties with null value. The order of calling this method, relative to the
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* {@code add()}/{@code addValue()} methods, is not significant.
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*
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* @since 12.0
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*/
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public ToStringHelper omitNullValues() {
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omitNullValues = true;
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return this;
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}
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/**
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* Adds a name/value pair to the formatted output in {@code name=value} format.
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* If {@code value} is {@code null}, the string {@code "null"} is used, unless
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* {@link #omitNullValues()} is called, in which case this name/value pair will
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* not be added.
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*/
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public ToStringHelper add(String name, @Nullable Object value) {
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return addHolder(name, value);
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}
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/**
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* Adds a name/value pair to the formatted output in {@code name=value} format.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper add(String name, boolean value) {
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return addHolder(name, String.valueOf(value));
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}
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/**
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* Adds a name/value pair to the formatted output in {@code name=value} format.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper add(String name, char value) {
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return addHolder(name, String.valueOf(value));
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}
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/**
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* Adds a name/value pair to the formatted output in {@code name=value} format.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper add(String name, double value) {
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return addHolder(name, String.valueOf(value));
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}
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/**
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* Adds a name/value pair to the formatted output in {@code name=value} format.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper add(String name, float value) {
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return addHolder(name, String.valueOf(value));
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}
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/**
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* Adds a name/value pair to the formatted output in {@code name=value} format.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper add(String name, int value) {
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return addHolder(name, String.valueOf(value));
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}
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/**
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* Adds a name/value pair to the formatted output in {@code name=value} format.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper add(String name, long value) {
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return addHolder(name, String.valueOf(value));
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}
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/**
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* Adds an unnamed value to the formatted output.
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*
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* <p>
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* It is strongly encouraged to use {@link #add(String, Object)} instead and
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* give value a readable name.
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*/
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public ToStringHelper addValue(@Nullable Object value) {
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return addHolder(value);
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}
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/**
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* Adds an unnamed value to the formatted output.
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*
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* <p>
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* It is strongly encouraged to use {@link #add(String, boolean)} instead and
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* give value a readable name.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper addValue(boolean value) {
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return addHolder(String.valueOf(value));
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}
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/**
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* Adds an unnamed value to the formatted output.
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*
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* <p>
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* It is strongly encouraged to use {@link #add(String, char)} instead and give
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* value a readable name.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper addValue(char value) {
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return addHolder(String.valueOf(value));
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}
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/**
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* Adds an unnamed value to the formatted output.
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*
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* <p>
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* It is strongly encouraged to use {@link #add(String, double)} instead and
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* give value a readable name.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper addValue(double value) {
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return addHolder(String.valueOf(value));
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}
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/**
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* Adds an unnamed value to the formatted output.
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*
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* <p>
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* It is strongly encouraged to use {@link #add(String, float)} instead and give
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* value a readable name.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper addValue(float value) {
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return addHolder(String.valueOf(value));
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}
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/**
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* Adds an unnamed value to the formatted output.
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*
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* <p>
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* It is strongly encouraged to use {@link #add(String, int)} instead and give
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* value a readable name.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper addValue(int value) {
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return addHolder(String.valueOf(value));
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}
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/**
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* Adds an unnamed value to the formatted output.
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*
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* <p>
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* It is strongly encouraged to use {@link #add(String, long)} instead and give
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* value a readable name.
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*
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* @since 11.0 (source-compatible since 2.0)
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*/
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public ToStringHelper addValue(long value) {
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return addHolder(String.valueOf(value));
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}
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/**
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* Returns a string in the format specified by
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* {@link Objects#toStringHelper(Object)}.
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*
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* <p>
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* After calling this method, you can keep adding more properties to later call
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* toString() again and get a more complete representation of the same object;
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* but properties cannot be removed, so this only allows limited reuse of the
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* helper instance. The helper allows duplication of properties (multiple
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* name/value pairs with the same name can be added).
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*/
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@Override
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public String toString() {
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// create a copy to keep it consistent in case value changes
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boolean omitNullValuesSnapshot = omitNullValues;
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String nextSeparator = "";
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StringBuilder builder = new StringBuilder(32).append(className).append('{');
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for (ValueHolder valueHolder = holderHead.next; valueHolder != null; valueHolder = valueHolder.next) {
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if (!omitNullValuesSnapshot || valueHolder.value != null) {
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builder.append(nextSeparator);
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nextSeparator = ", ";
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if (valueHolder.name != null) {
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builder.append(valueHolder.name).append('=');
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}
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builder.append(valueHolder.value);
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}
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}
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return builder.append('}').toString();
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}
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private ValueHolder addHolder() {
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ValueHolder valueHolder = new ValueHolder();
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holderTail = holderTail.next = valueHolder;
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return valueHolder;
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}
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private ToStringHelper addHolder(@Nullable Object value) {
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ValueHolder valueHolder = addHolder();
|
||||
valueHolder.value = value;
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return this;
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}
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private ToStringHelper addHolder(String name, @Nullable Object value) {
|
||||
ValueHolder valueHolder = addHolder();
|
||||
valueHolder.value = value;
|
||||
valueHolder.name = checkNotNull(name);
|
||||
return this;
|
||||
}
|
||||
|
||||
private static final class ValueHolder {
|
||||
String name;
|
||||
Object value;
|
||||
ValueHolder next;
|
||||
}
|
||||
}
|
||||
}
|
||||
Reference in New Issue
Block a user